In group communication the same information or service is delivered to multiple users. If many users are located within the same area, multicast or broadcast based transmission using, e.g., Multicast-Broadcast Multimedia Services (MBMS) is efficient. In MBMS, one or more services are broadcasted to intended users by using one or more shared communications resources.
When a wireless device located in some area wishes to enter into group communication, such as MBMS, the wireless device must first determine if a wanted service is being broadcasted in that area. Given that the service is available, it must then determine what communications resources that are used for broadcasting said service, e.g., what frequency bands and time slots that are being used to deliver the service, before it can start to participate in the group communication. These initialization steps take time, which means that there is a delay associated with a wireless device starting to participate in a group communication. It is of course desired to minimize the delay associated with a wireless device entering into group communication.
If wireless devices wanting to participate in group communication are spread over an area wider than a Multicast-Broadcast Single Frequency Network (MBSFN) area, the service or services have to be delivered over multiple MBSFNs. It is then highly desirable to provide service continuity between MBSFN areas, meaning that a group communication can continue without a need to reestablish ongoing group calls as a wireless device moves from one MBSFN to another MBSFN.
A service continuity method disclosed in 3GPP TS 23.468 v.13.0.0 March 2015, relies on a methodology to transfer group communication from multicast to unicast; in unicast there is one information stream broadcast for each intended user. A user or wireless device which is taking part in a group communication and which moves from a first to a second MBSFN area will, according to the method disclosed in 3GPP TS 23.468 v.13.0.0 March 2015, need to first have its communication transferred by the network from multicast in the first MBSFN area to unicast, and then back to multicast in the second MBSFN area. This is an inefficient way to provide service continuity and which may fail, e.g., when the unicast network is congested. Furthermore, transferring a user or wireless device to unicast requires that the wireless device connects to and/or registers with the network, which may not be possible, or may at least be undesirable.
It is therefore desired to provide a wireless communication system that reduces the delay associated with a wireless device entering into a group communication, and which is able to handle a situation when a user moves from one MBSFN to another during an ongoing group call without having to transfer the communication from multicast to unicast.